Various optical, photographic or printing materials use a near infrared absorbing dye. The near infrared absorbing dye has an absorption maximum (.lambda.max) within the near infrared region (900 to 1,100 nm). An ideal near infrared absorbing dye has no absorption within the visible region (400 to 600 nm).
An appropriate tool such as an infrared sensor can easily notice a near infrared ray, though the naked eye cannot see it. If an ink contains the ideal near infrared absorbing dye having no absorption within the visible region, the ink can record invisible information (character, image or the like) without disturbing visible information.
A sheet containing a near infrared absorbing dye is sometimes used as an optical filter. The near infrared absorbing sheet can substantially be transparent by using the ideal near infrared absorbing dye.
A silver halide photographic material is usually treated in an automatic developing machine. The machine has an infrared sensor of detecting the photographic material to conduct photographic treatment automatically. Japanese Patent Provisional Publication Nos. 1(1989)-266536, 3(1991)-226736 and European Patent No. 0703494A1 propose adding a near infrared absorbing dye to a silver halide photographic material to improve precision in detection of the material. Further, a near infrared sensitive silver halide photographic material should contain a near infrared absorbing dye as an antihalation dye, as is described in Japanese Patent Provisional Publication No. 63(1988)-55544. The near infrared absorbing dye used in a silver halide photographic material also preferably is an ideal dye having no absorption within the visible region to avoid influence on the exposure of light within the visible region or on the formed visible image.
Japanese Patent Provisional Publication Nos. 63(1988)-55544, 1(1989)-266536, 3(1991)-226736 and European Patent No. 0703494A1 disclose various near infrared absorbing dyes. However, the known near infrared absorbing dyes have remarkable absorption within the visible region.
The absorption maximum (.lambda.max) of a dye in the form of specific aggregates is longer than that of the same dye contained in a solution. This phenomenon about J aggregates of a spectral sensitizing dye used in silver halide photographic material is reported in H. T. James, The Theory of the Photographic Process, Macmillan Publishing Co., Inc., (1977), pages 218 to 222. If a near infrared absorbing dye is used in the form of specific aggregates, the absorption within the visible region (shorter than the infrared region) is reduced.
Even though the known near infrared absorbing dyes are used in the form of aggregates, the dyes still have remarkable absorption within the visible region.